We tried to evaluate the right ventricular function using a modified Swan-Ganz catheter with a rapid responsive thermistor. Twenty-four dogs comprised this series. Twelve were the model of left heart failure (Group A), and the other twelve were the model of right heart failure (Group B) produced by multiple ligation of coronary arteries. Dogs were studied for some of the circulatory indices before and after ligation with left atrial pressure at 10, 15 and 20mmHg in group A, and right atrial pressure at 10, 15 and 20mmHg in group B by volume loading. In group A, when the left atrial pressure was kept constant, right ventricular ejection fraction (RVEF) and right ventricular stroke work index (RVSWI) were decreased significantly after the ligation of coronary arteries. But there was no significant change in the peak right ventricular pressure-right ventricular endsystolic volume index ratio (peak RVP/RVESVI) associated with ligation. In group B, significant changes were observed in RVEF, RVSWI and peak RVP/RVESVI. Thus, it was found that right ventricular contractility in selective left heart failure was not reduced. E_max was considered to be a valuable index of ventricular contractility not affected by preload and afterload of ventricle, but this index is not easily measured clinically. The index peak RVP/RVESVI which is nearly equivalent to E_max, has an advantage in that it can be determined by the thermodilution method widely used in general. We conclude that this index is very useful to us for post-operative care in cardiac surgery.